Mechanical generators of isochronous oscillations



May 28, 1957 J. CHEVALLEREAU MECHANICAL GENERATORS OF ISOCHRONOUSOSCILLATION$ Filed July 12, 1954 5 Sheets-Sheet 2 I uvvewmR 5124A!Cmcmuawna s am. 7.

ATTDHNEYS May 28, 1957 J. C'HEVALLEREAU MECHANICAL GENERATORS OFISOCHRONOUS OSCILLATIONS Filed July 12, 1954 3 Sh eets-Shaet 3 BY wATTDHNEYS United States Patent MECHANICAL GENERATORS OF ISOCHRGNGUSOSCILLATIONS Jean Chevallereau, Lavallois-Perret, France, assignor toOliice National dEtudes et de Recherches Aeronautiques 0. N. E. R. A.,Chatillon-sous-Bagnenx, France, a society of France Application July 12,1954, Serial No. 442,6 36 Claims priority, application France July 31,1953 8 Claims. (Cl. 310-39) The present invention relates to precisionapparatus including at least one pendulum oscillating about an axis andsubjected to the action .of resilient return means and means fortransmitting rotation impulses to said pendulum to maintain theoscillating movement thereof.

My invention is more especially but not exclusively concerned withapparatus of this kind intended to be mounted on a moving body subjectedto high axial accelerations, which is the case in particular of someapparatus (chronometric apparatus, frequency reducing relays, etc.),intended to be mounted in self-propelled missiles so as automatically tocontrol the operation of other apparatus (signal transmitters,photographic or other cameras, recorders, igniting devices, etc.) eitherat a predetermined time or at predetermined time intervals.

The chief object of my invention is to provide :a device of this kindwhich is better adapted than those used up to the present time to meetthe requirements of practice and, in particular, which is not sensitiveto high accelerations.

Preferred embodiments of my invention will be hereinafter described withreference to the accompanying drawings given merely by way of exampleand in which:

Fig. 1 is .a diagrammatic axial sectional view of a chronometricapparatus made according to the invention.

Fig. 2 is a diagrammatic transverse section on an enlarged scale of thisapparatus substantially on the line IIII of Fig. l, the transmissioncontact being made according to a modification.

Fig. 3 is a transverse section on the line III--IH of Fig. 1.

Fig. 4 shows, similarly to Fig. 3, the transverse section of anapparatus made according to a modification of Figs. 1 to 3.

Figs. 5 to 7 each show a difierent modification of a detail of Fig. 2.

Fig. 8 is a diagrammatic perspective view of the combination of achronometric apparatus A, a frequency modifying relay B and a signaltransmitter C, according to my invention.

Fig. 9 is an axial sectional view of a relay analogous to that of Fig.8.

Figs. 10 and 11 are sectional views respectively on the lines X--X andXI-Xl of Fig. 9.

Fig. 12 shows in axial sectional view a signal transmitter analogous tothat of Fig. 8.

Fig. 13 is a sectional view on the line XIII-QCIII of Fig. 12.

Fig. 14 is a perspective view of the detail of the core and of themagnetic armature of the apparatus of Fig. 12.

An apparatus made as shown by the drawing essentially includes apendulum, means for sustaining the oscillating movement of said pendulumand means for resiliently urging this pendulum toward a middle angularposition.

The pendulum is essentially constituted by a piece 1 (Figs. 1 and 2)preferably in the form of a body of revolu- :tion, rigid with a pivotaxis or spindle 2 mounted in ice bearings 3 and 4 provided in elementsrigid with the casing 5 of the apparatus, which is made of an insulatingmaterial.

The means for maintaining the oscillating movement of pendulum 1 consistof a plate 6 rigid with pendulum 1 and made of soft iron or an analogousmetal carrying, at to each other, two pairs of symmetrical teeth 7a 7band 8a, 8b and of two pole pieces 9 and 10 mounted at 180 to each otheron casing 5, said pole pieces forming the ends of a U-shaped armaturei1. Pole pieces 9 and 10 are periodically polarized by a coil 12 whichis advantageously disposed along the axis of the casing, between thebranches of armature 11. A core 13, disposed inside coil 12 and carriedby the middle or bottom branch of armature 11, and held at the top by across member 14, extends through plate 6 in such manner as to make thepull in the axial direction practically negligible. Bearing 4 isprovided in the end of said core 13.

The periodically energizing circuit for coil 12, which isdiagrammatically shown on the left hand side of Fig. 8, includes abattery 15 or any other source of current the negative terminal of whichis connected through a conductor 16 with one of the terminals of thecoil and the positive terminal of which is connected with the otherterminal of the coil through a switch 15a, bearing 3, spindle 2,pendulum 1 and oscillation maintaining contacts 3331 adapted to closethe electric circuit on every half-oscillation of the pendulum, eitherdirectly to the pendulum, or as shown by Fig. 1 through a plate 18carried by spindle 2. A resistance 19 may be mounted in shunt across theterminals of coil 12 in order to eliminate sparks between contacts 3133.

The resilient return means of the pendulum may be constituted as inwatches or clocks by a spiral spring of great length. But thisarrangement involves some drawbacks. In particular, the adjustment ofthe characteristics of the spring necessitates a modification of thelength thereof and consequently causes a modification of the middleangular position of the pendulum with respect to the pole pieces, whichmodification requires a new adjustment. Furthermore, the central portionof the spiral spring is very flexible and an acceleration, evenmoderate, is capable of deforming it, thus modifying its characteristicsand therefore preventing the apparatus from working correctly and evenstopping it in the application which is being considered to movingbodies having a high axial acceleration.

In order to obviate these drawbacks, according to my invention, themeans for resiliently returning the pendulum consist of a pair ofsprings mounted in opposition, such an arrangement being designatedunder the name of push-pull spring mounting.

Such a resilient return system can be adjusted by acting simultaneouslyupon the two springs of each pair and therefore without modifying themiddle angular position of the pendulum. Furthermore, such a returnsystem is practically unsensitive to high accelerations to which it maybe subjected.

According to a first construction, I make use to constitute the returnsystem for the pendulum of helical springs mounted in opposition bypairs and for instance to two such springs 20a and 20b, as shown byFig. 1. These springs are fixed by one end to the pendulum along thesame diameter thereof, preferably close to its axis of rotation, forinstance to pins 21a and 21b, mounted between pendulum 1 and disc 18 andthey are fixed at the other end to supports fixed to casing 5 in anadjustable manner.

These supports may be constituted as shown in detail by Fig. 3. Theyconsist of small bars 22a, 22b which are fixed respectively to the twobranches of a U-shaped pie: 23 carried by easing 5, the middle portionof this tJ-shaped piece being advantageously used to receive the bearing3 of the pendulum. Bars 22a, 22b may be fixed on the U-shaped piece bymeans of screws 24a, 2412 engaged in longitudinal grooves 25a, 25bprovided in the bars. Screws 26a, 27a and 26b, 27b are provided toadjust the position of the bars and, when this adjustment has been made,to fix said bars in'the desired position, the whole in order to adjustthe strength of the springs Zita, 28b. Of course the springs might bemounted on supports making it possible to balance the two springsautomatically and to adjust them simultaneously.

It should be noted that even if the electric contact between bearing 3and pivot 2 is not very good, the feed circuit of coil 12 remains closedbetween said bearing and pendulum 1, through U-shaped member 23, bars22, springs 29 and pins 21.

According to another construction, the means for re siliently returningthe pendulum consist of V-shaped springs mounted in opposition by pairs,the system including for instance four such springs 28a, 28b, 28c, 280.,as shown by Fig. 4. These springs are preferably given a section whichis flat in the direction perpendicular to their middle plane. Thesesprings are fixed at one end to the pendulum along the same diameter,for instance by means of clips, 29a, 2% carried by the pendulum 1(located above the plane of the section of Fig. 4), and at the other endto clips 39a, 30b carried by easing 5, for instance through U-shapedpiece 23. Adjustment of the frequency of the pendulum can be obtainedeither by modifying the fixation of the springs on clips 29 and/or 30,or by means of masses adjustable in position in the radial direction onsaid movable system.

According to another feature of my invention which is supposed to beapplied to an apparatus of the same kind as above referred to, includinga pendulum the movement of which is maintained by the periodicalenergizing of a magnetic circuit, means are provided for giving thependulum at rest a relative angular position with respect to the polepieces such that energizing of the magnetic circuit starts theoscillating movement of said pendulum, the energizing circuit (which isclosed for said position of rest) being automatically opened as soon asthis oscillating movement is started.

According to an advantageous embodiment, said means are constituted byarranging the apparatus in such manner that in the state of rest thecontacts of the energizing circuit for maintainin oscillation move thependulum away from the balanced position it would assume under the onlyeifect of its return system. Such a balanced posi tion is shown forteeth 7 and 8 in dotted lines on Fig. 2 and in this position plate 6would be disposed symmetrically with respect to pole pieces 9 and 10 andconsequently the attraction forces on teeth 7 and 8 of plate 6 wouldbalance each other without starting the oscillation movement if theenergizing circuit were closed by means of switch 15a.

For this purpose, the oscillation maintaining contact includes thefollowing elements:

On the one hand, a contact finger 31 carried by the casing of theapparatus so that it can move with respect thereto with a rotating oranalogous movement; for instance, this finger is pivoted about spindle32 (Figs. 1 and 2) rigid with the casing;

And on the other hand, a contact stud 33 carried by the pendulum (forinstance by plate 18 which is fixed with this pendulum), this stud beinglocated for said balanced position in the plane passing through thepivot spindle 2 of the pendulum and the spindle 32 of the contactfinger.

Contact finger 31 is subjected to the action of a return system whichtends to bring it into the plane passing through axes 2 and 32. Due tothe thickness of finger 31 and stud 33, the oscillation maintainingcontact causes the oscillating system and in particular disc 6 to rotatethrough an angle on either in the direction indicated by Fig. 2 or inthe opposed direction, according as contact finger 31 is located on theside of stud 33 shown by the drawing or on the opposed side.

Thus, in the state of rest, that is to say when the energizing currentis cut off by switch 15a, plate 6 can take either of two positions, bothdissymmetrical with respect to pole pieces 9 and 10. If now theenergizing circuit is closed through switch 15a, the disc is urgedtoward the magnetically balanced position of the system, that is to sayin the direction of the arrow P Fig. 2. The oscillating movement istherefore truly started.

The resilient return means for contact finger 31 may be made indifferent ways:

According to a first construction, this return system is constituted ina fashion analogous to that of the oscillating system (pendulum), thatis to say by means of two springs 34a, 34b in opposition (Fig. 2), thesesprings being preferably helical springs. One end of each of thesesprings is fixed to a pin 35a, 35b carried by contact finger 31 and theother end to a pin carried by casing 5.

According to another construction, the return system is constituted by atorsional spring 36 (Figs. 5 and 6) forming a loop around axis 32 andadapted to bear both upon a surface 37 rigid with finger 31 and upon atleast one lug 38 rigid with casing 8. During operation, finger 31 iscaused to swing and each of the branches of spring 36 bears alternatelyupon the fixed finger or one of the fixed fingers 38. As spring 36 isslightly prestressed, finger 31 is strongly urged toward the restposition that is shown, where it is then kept without being able tooscillate.

According to a third construction, finger 31 is provided with two slots39a, 3% (Fig. 7) engaged on projections 40a, 49b carried by easing 5 andit is urged by two springs 41a, 41b. .During operation, finger 31 swingsand bears alternately upon pins 40a and 40b passing through the positionof rest where it bears simultaneously upon both of these pins withoutbeing able to oscillate. This device gives a very short time of contactbetween finger 31 and stud 33, which is also favorable to a goodoperation of the apparatus.

According to still another feature of my invention, which is supposed inthe present description to be applied to an apparatus such as abovedescribed, said apparatus is so arranged that its oscillating system andthe resilient return means thereof are symmetrical with respect to theaxis of oscillation of the pendulum and the centre of gravity of thewhole of the pieces in movement remains substantially upon said axis.

Thus, in the construction illustrated by the drawings, the followingelements are arranged in a symmetrical fashion with respect to theoscillation axis: pendulum 1, spindle 2, plate 6, disc 18, fingers 33 onthe one hand, and springs 20 with their pins 21 on the other hand.

When the apparatus is mounted on a movable body, such as aself-propelled missile, subjected to high axial accelerations, said axisof oscillation of the system is disposed parallel to the direction alongwhich these axial accelerations are produced, whereby the apparatusaccording to my invention is protected against the action of theseaccelerations and the oscillations are perfectly regular.

A chronometric apparatus as above described works in the followingmanner:

In the state of rest, switch 15a being open, the oscillating systemoccupies, as above explained, the position shown on Fig. 2 (or aposition symmetrical with respect thereto) When switch 15a is closed,the oscillating movement is started in the direction of arrow F. Stud 33passes beyond finger 31 and contact between 31 and 33 .is then cut off.Current ceases to flow through the circuit. The pendulum keeps movingagainst the action of springs 20a, 205, then stops under the effect ofthese springs and returns in the opposed direction, also under thisaction. Contact is again established for a very short time betweenfinger 31 and stud 33, this stud being then above finger 31. The platethen occupies a position which is dissymmetrical with respect to polepieces 9 and 10 and it is urged in the direction which accelerates itsmovement. The oscillating movement is thus constantly maintained as longas switch a remains closed. Thus, two contacts and two pulls areobtained for every cycle or period.

The advantages of this apparatus are in particular as follows:

It is not responsive, from the point of view of the frequency ofoscillations, to the action of accelerations which may be as high as 150g and parallel to the axis of oscillation of the system. Starting of thedevice is automatic and its frequency adjustment is very accurate. Itsconstruction is very compact so that it can be mounted in a sealed bulbunder vacuum or in an inert atmosphere.

Such a chronometric apparatus may be used as a clock or watch byassociating thereto any device for transforming the oscillating movementinto a circular movement, as Well known in the art.

However, such an apparatus is preferably used to transmit signals of afrequency equal to the frequency of oscillation or to twice thisoscillation frequency, for which purpose for instance I make use eitherof transmission contacts 4217 (Fig. l) analogous to oscillationmaintaining contacts 33-31, or of two elastic contacts 43a, 4319 (Figs.2. and 8) cooperating with a contact 44 carried by pendulum 1, theoscillating system being itself connected twice per cycle to thepositive terminal of battery 15. In this last case, if contacts 43a, 43bare connected together through a circuit leading to a point 45 (Fig. 8)and provided with a switch 46, it is possible to receive at this pointone or two impulses per cycle according as switch 46 is opened orclosed.

The impulses thus transmitted may be either used directly to start theutilization apparatus (signal transmitters, photographic cameras,recorders, etc.), or sent to apparatus for dividing or possiblymultiplying the frequency, the impulses emitted in turn by these lastmentioned apparatus being then capable of starting utilizationapparatus.

For instance, I may associate with the chronometric apparatus A (Fig. 8)a frequency divider B, the impulses emitted by this last mentionedapparatus being sent to a utilization apparatus such as an opticalsignal transmitter C.

Concerning the frequency divider B, it advantageously includes anoscillating member analogous to that of apparatus A, the oscillations ofwhich are maintained by impulses transmitted from said apparatus A. A

The elements of the frequency divider which are analogous to those ofthe chronometric apparatus have been designated by the same numeralswith index 1 (Figs. 9 to 11). Plate 6 can oscillate between twoadjustable abutments 47 and 48 (Fig. 11). Opposed springs m and 20b1urge the plate toward abutment 47.

Coil 121 is connected on the one hand directly to point 45 and on theother hand to the negative terminal of battery 15 through wire 16,without making use of course of an oscillation maintaining contact. Itwill be understood that the impulses received by coil 121 cause theplate to turn toward its abutment 48.

Disc 61 is provided with pawl and ratchet means capable of transformingits oscillation movement into an intermittent rotary movement, thesemeans including for instance a ratchet wheel 49 (Fig. 10) mounted on ahollow shaft 50 so as to be able to rotate with respect to spindle 21, apawl 51 mounted on the plate and adapted to drive the ratchet wheel in apredetermined direction, and finally an adjustable pawl 52 carried byU-shaped member 231 and adapted to prevent rotation of the ratchet wheelin the opposed direction. provided inside hollow shaft 50.

At the upper part of hollow shaft 50, there is fixed a plate 53 on whichis disposed a rotary distributor including a transmission contact finger54 journalled on plate 53 and urged radially by a helical spring 55,this contact finger cooperating with one or several studs 56 carried bythe insulating casing 51.

By way of modification, the transmitting contact may be established in afashion analogous to the oscillation maintaining contact 17 of thechronometric apparatus.

This frequency dividing apparatus works in the following manner:

On every impulse received at point 45, plate 61 has a to and fromovement and ratchet wheel 49 turns through an angle [3 equal to afraction l/n of one revolution, n being the number of teeth of ratchetwheel 49, which therefore makes one revolution for n impulses. On everystud 56, there is received only one impulse for the n impulses receivedat point 45. If p studs 56 are provided, p being a sub-multiple of n andsaid studs being distributed at equal distances on casing 51 andconnected together at a point 57, there is received at this point only 2impulses on the n impulses received at point 45. It is thus possible toobtain a frequency division according to a ratio p/n, which ratio can bedetermined at will and by suitably choosing the number of teeth of theratchet wheel 49 and the number of studs 56 connected together.

The advantages of such a frequency dividing apparatus are as follows:

It has a longitudinal axis in the direction of which all the movablepieces are adapted better to resist mechanically to accelerations. Itselastic systems are themselves protected against said accelerations.Therefore in an apparatus mounted on a body subjected to high axialaccelerations, the frequency dividing apparatus will be disposed so thatsaid axis thereof is parallel to the direction of said accelerations.Therefore it has a compact shape making it possible to mount it in asealed bulb under vacuum or in an inert atmosphere.

Finally, the utilization apparatus C to be energized 'by the impulsestransmitted from the frequency dividing apparatus B (or possiblydirectly by chronometric apparatus A) preferably includes a pendulumsubjected to resilient return means and :said utilization apparatus isarranged in such manner that its oscillating system and the resilientreturn means for this system have their centre of gravity substantiallyon said axis.

It is essentially constituted by a cylindrical armature 58 and a centralcore 59 between which there is disposed a coil 60 (Figs. 8 and 12 to14). This coil is fed, through insulated terminals 61, 62 extendingthrough the bottom 63 of the apparatus, on the one hand by means of awire 64 connected to the point 57 of the frequency dividing apparatusand on the other hand by means of a wire 65 connected to a negativeterminal of battery 15 through for instance wire 16. A reactance may beprovided in parallel with coil 60.

The oscillating system of the apparatus is advantageously constituted bya plate 67 which is fixed by its opposed ends 68a, 68b to armature 58,by means for instance of screws 6%, 69b engaged in screw-threaded holes70a, 70b provided in said armature. The body of plate 67 is connected toits ends 68a, 6817 through thinner portions which enable most of theplate to oscillate substantially along an axis ab passing through theheads of fixation screws 69a, 6%.

I provide on the ends of armature 58 and core 59 recessed portions 71and 72 intended both .to limit the zone of attraction of the armature onthe plate to the portion of the armature which is not recessed and toenable most of the plate to rotate about axis ab.

The external face of the plate carries a mirror 73 capable of reflectingthe light rays transmitted into the apparatus through a transparentwindow 74 provided in Bearing 31 is the cap 75 which constitutes witharmature 58 and bottom 61' the casing of the apparatus. On the otherface of the apparatus,-I provide masses 76 adapted to balance the mirror73 and its support so that the centre of gravity of the wholeoscillating system (which also forms its own return system) is broughtback onto the axis of oscillation ab. 7

By way of modification, the plate might be pivoted on an axis and fittedwith an independent return system.

The operation of the apparatus is as follows: Upon every signaltransmission from coil 60, the portion 77 of the armature 58 attractsthe corresponding portion of plate 67. At the end of the signaltransmission, the plate is returned by its own elasticity against itsabutment 78 ('Fig. 12) provided on the recessed portion 71 of thearmature. This oscillation has for its effect to change the inclinationof the light rays reflected by mirror 73, which may sensitize arecording band.

The advantages of this apparatus are in particular the simplicity of itsconstruction and the fact that it is not responsive to highaccelerations Whatever be their direction.

In a general manner, while I have, in the above description, disclosedwhat I deem to be practical and efficient embodiments of my invention,it should be well understood that I do not wish to be limited thereto asthere might be changes made in the arrangement, disposition and form ofthe parts without departing from the principle of the present inventionas comprehended within the scope of the accompanying claims.

What I claim is:

1. A mechanical generator of isochronous oscillations which comprises,in combination, a casing, a pendulum journalled in said casing about anaxis fixed with respect to said casing, spring means interposed betweensaid casing and said pendulum to cause oscillation of said pendulumabout said axis at a frequency determined by said spring means,electro-magnetic means carried by said casing, for periodicallytransmitting rotation impulses in opposed directions to said pendulumabout said axis to maintain the oscillating movement thereof, meanscarried by said casing and responsive to the oscillation of saidpendulum for controlling said electro-magnetic means, the whole of themoving parts of said apparatus having its centre of gravity on saidaxis, and said pendulum and said means being symmetrical about saidaxis, said spring means being arranged for constantly urging saidpendulum toward a mean position thereof, said electro-magnetic meansbeing adjusted to act on said pendulum as it is passing through saidposition, and means for biasing said pendulum in either direction Withrespect to said position.

2. For use on a body having a longitudinal axis and intended to undergohigh accelerations in the direction of said axis, a mechanical generatorof isochronous oscillations which comprises, in combination, a casing,21 pendulum journalled in said casing about an axis fixed with respectto said casing, spring means interposed between said casing and saidpendulum to cause oscillation of said pendulum about said axis at afrequency determined by said .spring means, electromagnetic meanscarried by said casing, for periodically transmitting rotation impulsein opposed directions to said pendulum about said axis to maintain theoscillating movement thereof, means carried by said casing andresponsive to the oscillation 'of said pendulum for controlling saidelectro-magnetic means, the whole of the moving parts of said apparatushaving its centre of gravity on said axis, and said pendulum and saidmeans being symmetrical about said axis,

said spring means being arranged for constantly urging 1 means forbiasing said pendulum in either direction with r respect to saidposition.

3. For use on a body having a longitudinal axis and intended to undergohigh accelerations in the direction of said axis, a mechanical generatorof isochronous oscillations which comprises, in combination, a casing, apendulum journalled in said casing about an axis fixed with respect tosaid casing, spring means interposed between said casing and saidpendulum to cause oscillation of said pendulum about said axis at afrequency determined by said spring means, electro-magnetic meanscarried by said casing, for periodically transmitting rotation impulsein opposed directions to said pendulum about said axis to maintain theoscillating movement thereof, means carried by said casing andresponsive to the oscillation of said pendulum for controlling saidelectro-magnetic means, the whole of the moving parts of said apparatushaving its centre of gravity on said axis, and said pendulum and saidmeans being symmetrical about said axis, said spring means beingconstituted by at least two springs mounted in opposition, that is tosay in push-pull fashion, said spring means being arranged forconstantly urging said pendulum toward a mean position thereof, saidelectro-magnetic means being adjusted to act on said pendulum as it ispassing through said position, and means for biasing said pendulum ineither direction with respect to said position.

4. For use on a body having a longitudinal axis and intended to undergohigh accelerations in the direction of said axis, a mechanical generatorof isochronous oscillations which comprises, in combination, a casing, apendulum journalled in said casing about an axis fixed with respect tosaid casing, spring means interposed between said casing and saidpendulum to cause oscillation of said pendulum about said axis at afrequency determined by said spring means, electro-magnetic meanscarried by said casing, for periodically transmitting rotation impulsein opposed directions to said pendulum about said axis to maintain theoscillaing movement thereof, means carried by said casing and responsiveto the oscillation of said pendulum for controlling saidelectro-rnagnetic means, the whole of the moving parts of said apparatushaving its centre of gravity on said axis, and said pendulum and saidmeans being symmetrical about said axis, said spring means beingconstituted by at least two helical springs mounted in opposition, thatis to say in push-pull fashion, said spring means being arranged forconstantly urging said pendulum toward a mean position thereof, saidelectro-magnetic means being adjusted to act on said pendulum as it ispassing through said position, and means for biasing said pendulum ineither direction with respect to said position.

5. For use on a body having a longitudinal axis and intended to undergohigh accelerations in the direction of said axis, a mechanical generatorof isochronous oscillations which comprises, in combination, a casing, apendulum journalled in said casing about an axis fixed with respect tosaid casing, spring means interposed between said casing and saidpendulum to cause oscillation of said pendulum about said axis at afrequency determined by said spring means, electro-magnetic meanscarried by said casing, for periodically transmitting rotation impulsein opposed directions to said pendulum about said axis to maintain theoscillating movement thereof, means carried by said casing andresponsive to the oscillation of said pendulum for controlling saidelectro-magnetic means. the whole of the moving parts of said apparatushaving its centre of gravity on said axis, and said pendulum and saidmeans being symmetrical about said axis, said spring means beingconstituted by at least two V shaped springs mounted in opposition, thatis to say in push-pull fashion, said spring means being arranged forconstantly urging said pendulum toward a mean position thereof, saidelectro-magnetic means being adjusted to act on said pendulum as it ispassing through said position, and means for biasing said pendulum ineither direction with respect to said position.

6. A mechanical generator of isochronous oscillations which comprises,in combination, a casing, a pendulum journalled in said casing about anaxis fixed with respect to said casing, spring means interposed betweensaid casing and said pendulum to cause oscillation of said pendulumabout said axis at a frequency determined by said spring means,electro-magnetic means carried by said casing, for periodicallytransmitting rotation impulses in opposed directions to said pendulumabout said axis to maintain the oscillating movement thereof, meanscarried by said casing and responsive to the oscillation of saidpendulum for controlling said electro-magnetic means, the whole of themoving parts of said apparatus having its centre of gravity on saidaxis, and said pendulum and said means being symmetrical about saidaxis, said electro-magnetic means comprising an oscillating member rigidwith said pendulum and symmetrical about a plane passing through saidaxis, a magnetic circuit fixed on said casing and including two polepieces located on either side of said oscillating member for impartingrotation impulses thereto, a coil for energizing said pole pieces, anelectric circuit for feeding current to said coil, said pole piecesbeing shaped and energized to produce a field the resultant of which isalong a diametral line passing through said axis and at right anglesthereto, said spring means being arranged for constantly urging saidpendulum toward a mean position thereof, where said plane of symmetry ofsaid oscillating member passes through said resultant, saidelectro-magnetic means be- 10 ing adjusted to act on said pendulum as itis passing through said mean position, and means for biasing saidpendulum in either direction with respect to said position.

7. A generator according to claim 6 in which said means for controllingsaid electro-magnetic means include two contacts, one carried by saidpendulum and the other resiliently mounted in said casing, inserted insaid electric circuit for feeding said coil, the means for biasing saidpendulum being constituted by said resiliently mounted contact.

8. In combination, a mechanical oscillation generator according to claim1, an electric feed circuit, means operative by said pendulum foropening and closing said feed circuit to produce current pulses therein,and a motor fed with current from said circuit and including speedreducing gear means.

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